This application proposes to create and assess a new mode of active targeting for anticancer agents to solid tumors that develop an acidic extracellular environment. The current paradigm of active tumor targeting technology in chemotherapy is based on active internalization of drug carriers into cells by binding between a tumor specific antigen and its monoclonal antibody (mAb) or between a ligand and its corresponding receptor. In an attempt to shift this paradigm, an intelligent polymeric micelle system will be devised. The micelle will hide a particular moiety during circulation, which has the strong capability to translocate the micelle into cells, and expose the moiety in the tumor extracellular environment to facilitate the internalization process. Thus, micelle technology turns a non-specific cell internalizing vector into a tumor specific tool. For this purpose, the slightly acidic tumor extracellular pH (pHe: pH 6.6-7.0) has been selected as a triggering signal for exposure of the moiety because this acidity is natural in most solid tumors and is confined to extracellular space. This new system will broaden the range of solid tumors that can be treated using targeted chemotherapy and it is expected to replace cumbersome and expensive mAb-based targeting technology. The goal of this application is to design and construct a super pH-sensitive surface on a micelle core structure to provide exposure mechanisms for an internalizing agent. When this technology is successful, the micelle system will be capable of targeting anticancer drugs to most solid tumors that have pHe values below 7.0. This triggering pH was found to be reasonable, judging from our feasibility results obtained from two different micelle systems. In this application, a model cell penetrating peptide (CPP) TAT is utilized, which does not require particular antigens or receptors for cellular localization. [unreadable] [unreadable] [unreadable]